BMI Calculator

Understanding BMI

BMI (Body Mass Index) is a simple screening tool calculated from height and weight: BMI = weight(kg) / height(m)². Standard categories: Underweight < 18.5 · Normal weight 18.5–24.9 · Overweight 25–29.9 · Obese ≥ 30. BMI is widely used in clinical settings because it's easy to calculate, but it has limitations — it doesn't distinguish between muscle and fat, and may misclassify muscular athletes as overweight.

For a more complete picture, combine BMI with waist circumference (men > 40 inches and women > 35 inches indicate elevated health risk regardless of BMI), body fat percentage, and other clinical measures.

Frequently Asked Questions

• Is BMI an accurate measure of health?
  BMI is a useful population-level screening tool but has individual limitations. It overestimates fatness in muscular people (athletes) and underestimates it in people with low muscle mass (some elderly). It also doesn't account for where fat is distributed — visceral fat (around organs) is more metabolically harmful than subcutaneous fat.
• What is a healthy BMI range?
  For most adults, 18.5–24.9 is considered healthy. For Asian populations, the WHO recommends lower thresholds (overweight at 23+, obese at 27.5+) due to higher health risks at lower BMI values. Children use age- and sex-specific BMI percentiles rather than fixed cutoffs.
• What are the BMI categories for adults?
  BMI categories defined by the CDC and WHO are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (30 and above). Obesity is further divided into Class 1 (30–34.9), Class 2 (35–39.9), and Class 3 (40+). These thresholds apply to adults 20 and older; children use age- and sex-specific percentile charts.
• Does BMI differ for men and women?
  The same BMI scale applies to both men and women, but BMI can be misleading differently by sex. Women naturally carry more body fat than men at the same BMI. A man and woman with a BMI of 25 may have meaningfully different body fat percentages. For a more sex-specific measure, consider a body fat percentage calculator alongside BMI.

What BMI Tells You — and What It Doesn't

Body Mass Index is a quick screening number calculated from your height and weight: weight in kilograms divided by height in meters squared. The standard categories are underweight (under 18.5), healthy weight (18.5–24.9), overweight (25–29.9), and obese (30 and above). BMI is useful because it's fast, free, and correlates at the population level with health risks. But it's a screening tool, not a diagnosis — it doesn't measure body fat directly or distinguish muscle from fat, so it should be read alongside other measures, not in isolation.

Worked Example

A person who is 5'10" (1.78 m) and weighs 170 lb (77 kg) has a BMI of about 24.4 — within the healthy range. Add 20 pounds and the BMI rises to roughly 27, crossing into the overweight category. The calculator also estimates an ideal weight range for your height, giving you a concrete target band rather than a single number. Seeing how a 15–20 pound change shifts your category can help frame realistic goals.

Where BMI Falls Short

Because BMI uses only height and weight, it can misclassify certain people. A muscular athlete may register as "overweight" despite low body fat, while someone with little muscle can fall in the "healthy" range while carrying excess fat. It also doesn't capture where fat is stored — abdominal fat carries more health risk than fat on the hips and thighs, which is why waist circumference and body-fat percentage add valuable context. Use BMI as a starting point, then look at body composition, waist measurement, and how you feel and function to get the full picture.

• Is BMI accurate for athletes?
  Not always. Muscle weighs more than fat, so very muscular people can have a high BMI while carrying low body fat. For them, a body-fat measurement is more informative.
• What is a healthy BMI range?
  A BMI between 18.5 and 24.9 is generally considered healthy for adults. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese.
• Should I use BMI alone to judge my health?
  No. BMI is a screening tool. Combine it with body-fat percentage, waist circumference, activity level, and guidance from a healthcare provider for a complete assessment.